(MCT) AUSTIN, Texas—The cause of a fire that led to devastating explosions a month ago at a fertilizer plant in this small town north of Waco remains undetermined, state and federal investigators said at a news conference Thursday.

The April 17 fire at the West Fertilizer Co. led to two explosions of ammonium nitrate at the site, milliseconds apart, leaving a crater 93 feet wide and 10 feet deep, authorities said.

Fourteen people were killed in the blasts, more than 200 were wounded, and scores of homes were damaged or destroyed.

State Fire Marshal Chris Connealy said the chief fire-cause classifications — natural, incendiary or accidental — couldn’t be applied to the West Fertilizer Co. fire because investigators hadn’t proven a cause to an acceptable level of certainty and because multiple possible causes remain under investigation.

Connealy said investigators hadn’t ruled out an intentionally set fire, a malfunction involving the 120-volt electrical system at the site or a battery-powered golf cart parked in the seed room.

Investigators found two surviving pieces of a battery-powered golf cart — a brake pad and an axle. Such carts have a history of causing fires, said Brian Hoback, a member of the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, the lead federal agency in the investigation. Hoback wouldn’t say who owned the golf cart.

On behalf of West Fertilizer Co., attorney John McCoy issued a statement Thursday evening thanking investigators for their diligence and dedication.

“The authorities repeatedly emphasized that their investigation continues, as does ours. Out of respect to the various agencies and to assure that their investigations are not compromised, we will not offer any additional comments or opinions at this time,” McCoy said Evidence from the fertilizer plant was found as far as 2.5 miles away, though most of the debris from the facility was found within 3,000 feet of the blast site, Assistant State Fire Marshal Kelly Kistner said.

The ATF spent $500,000 on heavy equipment rental and more than $1 million overall on the investigation. Between the ATF and the state fire marshals office, more that 104 personnel have been involved in the investigation.

Investigators have combed through the plant’s roughly 14-acre sitepiece by piece. A silo of corn was sifted by hand. Buildings were dug out with heavy machinery. The crater was excavated. Using what they found, investigators created 3-D renderings of the site.

Investigations generally average no longer than a week, said Robert Champion, the special ATF agent in charge of the site. The West investigation, Champion said, is “one of the longest call-outs we’ve had.” The Texas Rangers and other agencies have been pulled into other aspects of the investigation.

A week ago, in an incident the U.S. Attorney’s Office hasn’t tied to the fertilizer plant explosion, 31 year-old West paramedic Bryce Reed was arrested and charged with unlawful possession of a destructive device. Reed has pleaded not guilty and remains in federal custody.

On the day of the blasts, firefighters had been dispatched to deal with the fire at 7:32 p.m., Kistner said. They arrived at 7:38 p.m. and at 7:41 p.m. requested additional help.

As the temperature in the facility increased, so did pressure, according to investigators.

Ammonium nitrate, stored in wooden bins, began changing states, making it more susceptible to heat. Falling equipment might have provided the necessary shock to prompt a blast, investigators said.

At 7:51 p.m., the explosions struck.

Investigators estimate that 28 to 34 tons of ammonium nitrate exploded — the equivalent of 15,000 to 20,000 pounds of TNT, Kistner said.

An additional 20 to 30 tons of ammonium nitrate inside the building didn’t explode. Roughly 100 tons stored in rail car on the site also didn’t explode, Kistner said.

Hoback said ammonium nitrate at the fertilizer plant was kept in wooden bins that “bumped up against the seed room.” Officials wouldn’t say whether the facility’s storage of ammonium nitrate violated any codes, but federal workplace safety standards require walls of ammonium nitrate storage buildings that are near combustible materials to be made of “fire-resistant construction.” It’s not clear whether West Fertilizer Co. met this standard.

What is more clear is that the storage building lacked a sprinkler system as required by national fire protection codes. However, McLennan County is prohibited by state law from adopting the code because of its small size.

Kistner wouldn’t comment on whether the state fire marshal’s office would support requiring counties to adopt a standardized fire code.

Daniel Horowitz, managing director of the U.S. Chemical Safety Board, told the American-Statesman that adoption of a fire code “would have offered some level of provision to prevent a fire around the ammonium nitrate.” Horowitz said the agency would continue to study the root cause of the accident to address how safety practices, from fire code implementation to ammonium nitrate storage practices, across the country can be improved. The board, which studies accident sites, wasn’t included in the news conference.

On North Main Street, just south of the fertilizer plant, which remains fenced off, most of the houses have nailed-in plywood in place of windows, garage doors are blown off, and bright green pieces of paper — leftover markers from searches by authorities — remain stuck to front doors.

One of these homes belongs to Bernard Gerik, 70, who said Thursday that the blasts blew Sheetrock off his walls and broke wall-studs loose.

The house itself “picked up and then sat back down,” Gerik said. He and nearly all his neighbors were in the street at the time of the explosion, he said, lured outside by the sound of fire engines and the ghastly vision of the fire about a half-mile away.

The house will take months to repair, so he and his wife will pack up to move in with their son outside of West, said Gerik, who didn’t seem terribly concerned about the latest news of the investigation into the blast.